The human body detecting device for the vehicles in this field is used in a system which controls opening and closing operations of a door of a vehicle, such as an automobile for detecting a human body approaching the vehicle. The system for opening and closing operations of a door detects a human body and automatically unlocks the vehicle door when the driver or the owner of the vehicle approaches the vehicle with an electronic key or card which can identify the driver or the owner. The system also locks the door when the driver or the owner of the vehicle gets off and operates a switch provided in the door handle.
One of a known human body detecting device of the type is shown in a publication (U.S. Pat. No. 6,075,294), in which the device uses an electrostatic capacitance of equivalent parallel flat plate electrodes between a sensor electrode provided in the door handle and a vehicle body (mostly the exterior panel of the door) and detects the change of the electrostatic capacitance occurring when an object having electromagnetic property (such as dielectric constant) different from that of the air, such as a human hand, is inserted between the door handle and the door exterior panel. This mechanism is used as a touch sensor or a switch element.
The principle of using electrostatic capacitance of equivalent parallel flat plate electrodes used as a touch sensor is known for example from JP 02-27637B2. Also known is a detection of the electrostatic capacitance change by a single conductive body, in place of a pair of parallel flat plate electrodes, used as a touch sensor. This method is shown in U.S. Pat. No. 3,689,814.
These known arts are not sufficient to achieve accurate detection operation because of unfavorable conditions in which a sensor electrode is placed in and which arise from the fact that the electrode is located within a door handle. Specifically, there tend to be a large variation in relevant parameters, such as the distance between a human body and the sensor electrode in the handle, and a direction in which the human body approaches the electrode, depending on how the human body approaches the door handle. Also, the electrostatic capacitance of the sensor electrode may change due to entering of water into the inside of door handle. In order to avoid such entering of water, a waterproof means such as sealing agent can be provided to the door handle. However, this will lead to an increased complexity of the device and will render the device less suitable for mass production. Further, there is also a problem of available space in the door handle.